1. Field of the Invention
The present invention relates to an indication display unit for vehicles which provides a driver with the whole information about the vehicle such as its velocity, revolution frequency of the engine, left-fuel quantity, clock, and other various alarm devices by projecting an image which will appear on a display device, to the reflecting surface on a reflecting means which is located forwardly of a driver seat.
2. Description of the Prior Art
The use of display units, provided with a projecting device, have been recently increased in order to save space for installation of an increasing number of display devices required for providing a driver with various driving information.
As an indication display unit for vehicles of this type, there is one in which a display device, included in an indicating image projector, is mounted inside the dashboard with its display surface facing upwards to a reflecting means, such as a semi-translucent mirror inclining towards the driver seat, where the reflecting means is installed on the dashboard, whereby a displayed image projected from the above display device of the indicating image projector is reflected on the surface of the reflecting means so as to be sighted there, that is, to be sighted ahead of the windshield of the vehicle (Japanese Utility model No. 50-48576).
However, the displayed image on the reflecting means can hardly be seen on the indication display unit of this conventional type when external strong rays of light are radiated to the above reflecting surface from outside the vehicle through the windshield, and another problem still remains that since other indication meters or devices are also installed in the dashboard, only limited space is available for installing the above type of indication display unit.
On the other hand, another kind of indication display device has also been introduced in order to avoid the above problems in which the display device is installed at the inner ceiling of the vehicle, whereby the displayed image projected therefrom is reflected by the reflecting means located forwardly of the driver (Japanese Utility Model No. 62-056666).
However, the indication display unit comprising an indicating image projector and a reflecting means normally adopts a high-bright fluorescent tube for its display device contained in the above projector so as to intensify the contrast of the reflected image on the reflecting means, whereby the scattered rays of light from the displaying surface 11a of the indicating image projector 11 are radiated to the ceiling surface 12 as shown in FIG. 4a. By this reason, the scattered light reflecting area 12a which is brightly illuminated is generated in the ceiling surface around the image projector 11 as shown in FIG. 4(b), and consequently the above area is also reflected on the reflecting surface, deteriorating the quality of the displayed image to be sighted thereon.
Furthermore, as shown in FIG. 10a, when a vehicle A following behind the vehicle B radiates a high-positioned beam from its head lamp, the ceiling of the vehicle B is illuminated through the rear window thereof, and also even when the beam from the vehicle A is low-positioned, the above ceiling thereof is also illuminated if vehicle B starts descending a slope.
Therefore, when a head-up display is installed for sighting of the image on the reflecting means projected from the display device of the indicating image projector, only the image projected therefrom is normally reflected as shown in FIG. 8(a), but once the vehicle is illuminated by another one following therebehind through its rear window, the projector 10 storing the display device and the ceiling surface 40 are illuminated as shown in FIG. 9, so that the illuminated images 10' and 40' of the indicating image projector 10 and the ceiling surface 40 respectively are reflected altogether around the reflected image, resulting in that the image of the indication can hardly be seen.
The present invention relates to an indication display unit for enabling a driver to sight an image on the reflecting means projected from the display device mounted on the ceiling of the vehicle, and its principal object is to provide a reflected image of good quality excluding bad effects on the displayed image to be reflected on the reflecting means caused by external light radiated from outside the vehicle.